1. Field of the Invention
This invention relates to a plastic retainer for roller bearing such as cylindrical roller bearing, conical roller bearing or spherical roller bearing.
2. Description of the Prior Art
A plastic retainer for roller bearing generally widely known, for example, a plastic retainer for cylindrical roller bearing as shown in FIGS. 1 and 2 of the accompanying drawings, comprises two concentric annular members 11a and 12a facing each other, a predetermined number of posts 13a disposed circumferentially equidistantly, and a pocket 14a for containing a roller 2 formed between adjacent posts and the planar portion 121a of the two annular members. In Figures, reference numeral 3 designates an outer race and reference numeral 4 denotes an inner race.
Generally, a plastic retainer is lighter in weight than a metallic retainer and has resilience and has been regarded as being higher in breaking strength under severe conditions involving vibration, shock, etc. than the metallic retainer, and also has been regarded as being different in the form of breaking from the metallic retainer.
However, according to the fatigue breaking test carried out by the inventors, it has been found that in the plastic retainer, as in the metallic retainer, concentrated stress occurs to the corner 15a of the connecting portion between the annular members 11a, 12a and the posts 13a and particularly, with the retainer outer peripheral portion or the retainer inner peripheral portion of the corner 15a as the starting point, the annular members are broken by crack being propagated toward the outer end surface of the annular member 12a as indicated by broken line B.
From this, it has been found that even in a plastic retainer, to avoid the concentration of stress and increase the strength, the shape of the corner 15a, particularly, the radius of curvature of the curved surface of the corner, is an important factor, but in the prior art, it has been necessary that the radius of curvature of the corner be set to a dimension which does not interfere with the chamfered portion of the roller contained in the pocket and therefore, it has been a very practical design to provide a uniform radius of curvature from the inner peripheral portion to the outer peripheral portion of the pocket.
Therefore, to improve the strength, the axial thickness and radial thickness of the annular members 11a and 12a have been increased, but such countermeasure is limited from the major dimensions (particularly, the width, inner diameter and outer diameter) of the bearing and in such a case, the roller dimensions are sometimes unavoidably made smaller and said thickness are increased, whereas this may give rise to a problem which may result in reduced load capacity of the bearing.
Thus, the conventional plastic retainer for roller bearing has been limited in the degree of freedom at the stage of designing.
The present invention has been made to solve the above-noted problems and an object thereof is to provide a plastic retainer for roller bearing which is high in breaking strength.
It is also an object of the present invention to provide a plastic retainer for roller bearing which is useful for the designing of a bearing of great load capacity and moreover is compact.
The invention will become fully apparent from the following detailed description thereof taken in conjunction with the accompanying drawings.